Electronic-scanning antennas



Nov. 17, 1970"" s. ZISLER 3,541,565

ELECTRONIC-SCANNING ANTENNAS Filed Sept. 6, 1967 3 Sheets-Sheet 1 3 Sheets-Sheet 5 Filed Sept. 6, 1967 E EM W TG CW ED LE EE 5F United States Patent 3,541,565 ELECTRONIC-SCANNING ANTENNAS Siegfried Zisler, Paris, France, assignor to CSF-Compagnie Generale de Telegraphic Sans iii], a corporation of France Filed Sept. 6, 1967, Ser. No. 665,885 Int. Cl. H0111 3/26, 19/06, 13/00 US. Cl. 343-854 4 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to directional electronicscanning antennas comprising a network of radiating elements distributed over a surface. In the conventional antennas of this kind, the radiating elements are arranged in one plane and the orientation of the beam from the antenna can be changed by introducing suitable phase-shifts between the different successive radiating elements.

Antennas of this kind thus require as many variable phase-shift elements as there are radiating elements, frequently a few thousands, and this is expensive.

On the other hand, the extent of the beam-scanning about the perpendicular to the plane of the antenna is limited to a comparatively low value, because of the increasing mismatch otherwise encountered and the increase in the level of the secondary lobes.

The present invention is aimed at overcoming these drawbacks.

According to the invention, there is provided an electronic-scanning antenna, of the type comprising a network of radiating elements distributed over a surface, and a utilization terminal to be connected to the utilization system of said antenna, wherein: said surface is a portion of a sphere; said antenna comprises a first and a second group of lossy feeders; said radiating elements are connected at the intersections of the feeders of said first group with the feeders of said second group; each feeder section connecting two consecutive elements has an electric length which is, at least approximately, equal to a whole multiple of the operating wavelength of said antenna; and wherein said antenna further comprises a switching system for selectively connecting any one of a predetermined group of said radiating elements to said utilization terminal.

The invention will be better understood, and other of its features rendered apparent by means of the following description and the appended drawing wherein:

FIG. 1 illustrates schematically, in plan, a part of the antenna in accordance with the invention;

FIG. 2 is a schematic view, along a feeder, of the antenna in accordance with the invention;

FIG. 3 shows explanatory diagrams;

FIG. 4 is a simplified diagram of the switching system for the antenna in accordance with the invention; and

FIG. 5 is a detailed diagram of an embodiment of the switch illustrated in FIG. 4.

FIG. 6 is a perspective view showing the location of the radiating elements over the sperical bearing surface.

The radiating elements 1.1, 1.2 8.3, 8.4 etc. of FIG. 1 are distributed over the surface of a sphere portion and connected at the intersections between the feeders 3,541,565 Patented Nov. 17, 1970 1001, 1002, etc. of a first group of lossy feeders and the feeders 2001, 2002 of a second group of lossy feeders; each element is represented by the respective unit digits, separated by a point, of the reference numbers of the two feeders to which it is connected. By lossy feeders are meant feeders whose losses are not negligibly small; the attenuation to be imparted thereby will be more precisely indicated hereinafter.

In FIG. 1, the feeders have been shown, for the sake of simplicity, as forming a network of square meshes, at the nodes of which the radiating elements are connected. This of course is not strictly speaking possible on the surface of a sphere, but the corresponding distribution of the radiating elements may be approximated for example through locating those elements at the intersections of the meridians and the parallels of a sphere, whose portion used for the antenna is symmetrical relatively to the corresponding equator plane.

FIG. 6 is a perspective view showing the corresponding location of the radiating elements over the bearing surface. In this figure the radiating elements are only shown by dots while the meridians and parallels are shown in dotted lines. The selective feeding means (in the case of a transmitting antenna) allow the direct feeding of, for example, one radiating element out of two along each meridian and each parallel, while the radiating elements other than the one which is directly fed by the feeder connecting it to the selective feeding means, are fed through the lossy feeders connecting the radiating elements along the parallels and meridians.

As for the feeders, it will be appreciated that each feeder section connecting two consecutive elements can, according to its length, be laid over various ones of the sphere arcs joining those elements and need not even contact the sphere over the whole of its length.

Those feeder sections are located inside the bearing surface or, where printed circuit technique is used, formed by an appropriate tracing over the inside face of this bearing surface.

Of course, the distance between consecutive radiating elements will generally be much smaller, relatively to the radius of the sphere to which the bearing surface belongs, as in the case in this figure.

FIG. 2 shows a section of the antenna along a feeder of FIG. 1.

In a first embodiment of the invention, the electric length of each feeder section, connecting two consecutive radiation elements, is equal to kx, where A is the operating wavelength of the antenna, and k an integer which is advantageously taken as small as possible taking into account the spacing of the radiating elements.

The operation is as follows:

When any element, which, irrespective of its reference number, will be called the center element 0, is connected to a source, all the elements around 0 are fed in phase. On the other hand, due to the losses introduced by the feeders, only those radiating elements, referred to as the active elements, which are sufiiciently fed, play a nonnegligible part in the radiation.

It may be considered, for example, that an element is active only as long as the power radiated thereby does not fall to less than about 20 db relatively to the power radiated by the centre point.

The active zone corresponding to a center element, will be defined as the region centered on this center element, which includes all the active elements.

If the radius over the sphere, a, of this active zone is sufficiently small relatively to the radius R of the sphere, the radiation diagram of the antenna defined by an active zone is substantially the same as that of a flat antenna, all of whose elements would be distributed over the plane tangent to the sphere at the centre point 0, this plane being shown by y'y in FIG. 2; the maximum of the diagram is directed along OX, normally to the tangent plane, i.e. along the radius of the sphere passing through 0.

More precisely, within an active zone of a given antenna in accordance with the invention, the radiation amplitude from each element of the antenna varies as a function of its distance from the center element approximately in accordance with the function F =(1r), where r is the ratio between the distance from the considered element to the center element and distance a, and where n is an exponent varying with the losses in the feeder lines.

In FIG. 3a the variation of the function -F when rv=2 is shown.

FIG. 3b shows the corresponding radiation diagram in a plane passing through OX (FIG. 2), the radiation power being expressed in dbs, as a function of the variable V where (p is the angle, expressed in degrees, between OX and a given direction of this plane (FIG. 2).

In order to change the orientation of the beam, it is merely necessary to switch the source to another centre point, i.e. to another radiating element. Provided that this element is at a distance of at least a from the edge of the antenna, the directional characteristics, secondary lobe levels and matching are not modified by this switching, unlike the case obtaining with scanning by means of a plane antenna.

Of course, it is assumed here that the radiating elements are more or less evenly distributed over the surface of the sphere portion and sufliciently numerous for the mean distance between two neighbouring elements to be small relatively to a.

The limitation of a relatively to R is necessary to reduce the secondary lobes and to limit the dimension of the active zone to a value which is compatible with the desired directivity.

FIG. 2 shows in adition that if all the radiating elements are fed in phase, it could only be deterimental to the radiation diagram to include in the active zone active radiating elements, whose distance to the plane y'y, tangent to the sphere at the centre point, is greater than M2. It will be readily seen that the condition Al )\2. for all the elements of the active zone is fulfilled for R (lcos arc sin \/2 However, although, as been said before, a must always remain limited, the last mentioned condition may be dispensed with if the radiation elements are not fed in phase, so that the phase shifts at the level of the radiating elements will compensate, at least partially, for the difference in the paths between the various radiating elements of the active zone and the plane tangent to the sphere at the centre point. Whether the condition Al 2 is fulfilled or not, a phase correction of this type allows an improvement of the radiation pattern relatively to an in-phase feeding.

It will be readily seen that such a partial compensation obtains if the electric length of the feeder section connecting two consecutive radiating elements is made somewhat inferior to k1, i.e. equal to kx-s, where 6 is a positive constant.

Of course the optimum precise value of 6 depends on the precise geometrical distribution and mean spacing of the radiating elements over the sphere portion, and on the value of k, but with the practical values which will generally be used, 6 will be found small as compared to A. In most cases, a good value of is given by:

with m1)\=distance between adjacent radiating elements. Once the beam-width, and consequently a has been chosen, the losses in the feeders are'adjusted, so as to obtain a correct distribution of amplitudes inside of the active zone and a negligible radiation for all the elements outside the zone with the radius a.

By way of example, a satisfactory antenna of the described type may be constructed with the following characteristics, for an operating wavelength 7\=l cm.

Beam-width (between half-power points): 2.

Scanning in latitude: 20.

Scaning in azimuth: 40

Width of the antenna: 60 cm.

Height of the antenna: 40 cm.

Number of radiating elements in an active zone: about Radius of sphere: 75A.

Radius of an active zone: 15%.

Total number of radiating elements: 3700.

Electrical length of each feeder section: 336".

It will generally be sufficient to provide a switching device for selectively connecting to the source each one of a predetermined group of the radiating elements.

If, for example, the beam width of the antenna is onedegree at half power, all that is necessary is to provide for the switching of radiating elements which are spaced at one degree intervals viewed from the centre of the sphere.

By way of example, it has been assumed that one element out of two (the elements numbered in FIG. 1) is to be selectively connected to the antenna feed system.

FIG. 4 illustrates the corresponding switching system.

The utilization system 4 (receiver, transmitter or transmitter/receiver as the case may be) is connected to the input 51 of the switch 5, which is the utilization terminal of the antenna. The switch 5 connects its input 51 to the input of one of the switches 100, 200 500, 600 in accordance with the signals applied to its control input 50 which is connected to a synchronization output 40 of the utilization system 4. Each switch 100 500, 600 connects its input 102 502, 602 to one of the radiating elements situated on the respective feeders 1001 1005, 1006 of the first set. The switches 100 500, 600 are controlled respectively by control signals fed to their control inputs 101 501,

601 the control inputs 101 501, 601 being connected to another synchronizing output 41 of the system 4.

This two-stage switching makes it possible firstly to select a feeder of one of the groups using the switch 5, then to connect a desired radiating element on this feeder to the utilization system 4, using the corresponding switch 100 500, 600.

A possible embodiment of the switches of the switching system, is illustrated in FIG. 5, where the switch 500 has been illustrated, assuming that the feeder 1005 contains only eight radiating elements which can be connected to the input 502.

The elements 5.1, 5.3 5.15 are grouped in pairs and connected by means of the two-position switches and 9 to the two-pole switches and 8; the input terminals of the two switches 8 are in turn connected to the input 502 through the two-position and switch 7. The control inputs 70, and of the respective switches 7, 8 and 9 are connected to the outputs of a synchronizing device 6 to which control signals are applied from the control input 501.

The switches 7 and 9 have been illustrated in the position and the switch 8 in the position, this results in element 5.5 being connected to the input 502.

A switching table can be drawn up, as follows:

For the switches 7, 8 and 9, switching diodes can for example be used.

The antenna in accordance with the invention allows a considerable economy of material. A fiat electronicscanning antenna with the same number of radiating elements would require a variable phase-shift element for each radiating element.

The invention is not limited to the embodiments which have been described here only by way of example.

What is claimed is:

1. An electronic-scanning antenna of the type comprising a network of radiating elements distributed over a surface and a utilization terminal to be connected to the utilization system of said antenna, wherein: said surface is a portion of a sphere; said antenna comprises a first and a second group of lossy feeders; said radiating elements are connected at the intersections of the feeders of said first group with the feeders of said second group; each feeder section connecting two consecutive elements has an electric length which is, at least approximately, equal to a whole multiple of the operating wavelength 7\ of said antenna; and wherein said antenna further comprises a switching system for selectively connecting any one of a predetermined group of said radiating elements to said utilization terminal.

2. An electronic-scanning antenna, as claimed in claim 1, wherein said radiating elements are located at the intersections of meridians and of parallels of said sphere,

3. An electronic-scanning antenna as claimed in claim 1, wherein the feeder sections connecting two consecutive radiating elements have an electric length exactly equal to k), where k is a positive integer, and wherein the losses in said feeders are such that when any element, referred to as the instantaneous centre element, 0, of said predetermined group of elements, is switched to said utilization terminal, the power emitted by any one of those radiating elements whose distance Al to the plane tangent to the sphere at O is higher than 7\/ 2, is negligible.

4. An electronic-scanning antenna as claimed in claim 1, wherein the feeder sections connecting two consecutive radiating elements have an electric length equal to k \-a, where k is a positive integer and 5 a positive constant which is small relatively to A.

U.S. Cl. X.R. 343754, 777 

